The present invention relates to an improvement of an internal combustion engine of the type having a main combustion chamber and an auxiliary combustion chamber so as to use the lean air-fuel mixture.
In order to decrease the content of the pollutants or toxic emissions such as carbon monoxide, unburnt hydrocarbons (HC), and nitrogen oxides (NOx) in the exhaust gases discharged from the internal combustion engines, there has been devised and demonstrated such a method as using the lean air-fuel mixture; that is, the air-fuel mixture with a high air-fuel ratio. However, because of its poor flamability and its low speed of combustion, the use of the lean air-fuel mixture generally results in the drop in engine efficiency and in the increase in fuel consumption rate (g/horsepower.hour).
To overcome these problems, there have been devised and demonstrated the internal combustion engines of the type having a main combustion chamber and an auxiliary combustion chamber communicated through a passage with the main combustion chamber. The air-fuel mixture compressed in the auxiliary combustion chamber is first ignited so that the combustion products or gases under an extremely high pressure may be injected through the passage at a high speed into the main combustion chamber. Therefore the air-fuel mixture in the main combustion chamber may be burnt quickly so that the speed of combustion in the main combustion chamber may be increased and the engine efficiency may be considerably improved.
However, the passage between the main and auxiliary combustion chambers must be relatively small in dimension so as to ensure an expected efficiency so that the complete scavenging of the auxiliary combustion chamber in the suction stroke is difficult to be attained. As a result, residual combustion products inevitably remain in the auxiliary combustion chamber. The residual combustion products dilute the air-fuel mixture which is pushed into the auxiliary combustion chamber through the passage from the main combustion chamber in the compression stroke so that the good ignitability of the mixture in the auxiliary combustion chamber by a spark plug cannot be ensured. To overcome this problem, various methods have been proposed. According to one method of the type disclosed in SAE paper No. 700491, the auxiliary combustion chamber is provided with a fuel injection nozzle so that a rich air-fuel mixture which has a good ignitability may be formed within the auxiliary combustion chamber. According to another prior method, the auxiliary combustion chamber is provided with an auxiliary suction valve so that an easily combustible air-fuel mixture may be formed within the auxiliary combustion chamber by additionally charging the rich air-fuel mixture through the auxiliary suction valve. However, the above two methods have a common defect that two air-fuel mixtures of different air-fuel ratios must be provided so that the fuel supply system is inevitably complex in construction, resulting in the difficulty in the control of the fuel supply and the increase in cost.